Aldehyde condensates, and particularly phenol-formaldehyde condensates were one of the first man-made resins ever to be produced. Phenol-formaldehyde resins have found wide acceptance for making molding compounds because they involve readily available materials and have good di-electric properties. All of the phenol-formaldehyde molding compounds that we are aware of include organic fillers. Wood flour is most commonly used for a number of reasons, including the facts that: the wood flour is inexpensive and has the desirable property of absorbing water that is liberated during the reaction, and there is a known chemical reaction of coupling with the saw dust to provide strength. A considerable amount of heat is liberated during the reaction of phenol and formaldehyde. One of the principal problems that has been involved in the process of making phenol-formaldehyde resins has been the control of the process to keep the temperature from running away and the resin from setting up in the reactor. For this reason and others, the commercial production of phenol-formaldehyde resins has been carried out in a liquid phase in batch reactors having extensive cooling coils and/or jackets, and in addition have been carried out in aqueous solutions, so that the flashing of water from the mixture can be utilized to further control the reaction. Reactions in the aqueous phase comprising approximately 40 to 50% water, require a couple of hours before it reaches the A or B prepolymer stage. The prepolymer is then blended with other materials, as for example, fillers. In the prior art processes wherein the reaction is carried to or approaching a B-stage, the reaction is controlled by utilizing a deficiency of formaldehyde, so that the reaction automatically terminates without crosslinking. Such materials are dried in the reactor, are poured from the reactors in a molten condition and are powdered. This novolak powder is then mixed with a solid hydrogen acceptor, as for example, hexamethylenetetramine to form a powder mixture which will crosslink into a C or an infusible state. Practically all phenol-formaldehyde molding powders that we are aware of are of the novolak type. One of the reasons this is so is that resoles tend to be so sticky and tacky that problems exist in handling and molding mixtures of fillers and conventional resoles.
Resole aldehyde condensate resins have been used heretofore principally as adhesives for making plywood, for binders of highly porous fiber mats, and for making foams from which the water of dilution and of reaction can be easily vented.
In this prior art background, the present invention was made.
An object of the present invention is the provision of a new and improved process of making molding compounds wherein the starting monomers can be transformed into a molding compound within a matter of minutes.
Another object of the present invention is the provision of a new and improved process of polymerizing monomers, and particularly aldehyde condensates, in a continuous controllable process as opposed to a batch process.
A further object of the present invention is the provision of a new and improved process of polymerizing resins having improved controllability, by reason of better heat transfer, and physical control of the reactants, as will be seen from the following description.
A still further object of the present invention is the provision of a new and improved process for making sheet molding compound which is much simpler, more economical, and faster to complete.